Radiation-sensitive emulsions employed in photography are comprised of a dispersing medium, typically gelatin, containing embedded micro-crystals--known as grains--of radiation-sensitive silver halide. A great variety of both regular and irregular grain shapes have been observed in silver halide photographic emulsions. Regular grains are often cubic or octahedral in shape. Grain edges may exhibit rounding due to ripening effects, and in the presence of strong ripening agents, such as ammonia, the grains may even be spherical. Rods and tabular grains in varied proportions have been frequently observed mixed in among other grain shapes, particularly where the pAg (the negative logarithm of silver ion activity) of the emulsions has been varied during precipitation, as occurs, for example, in single jet precipitations. Tabular grains are those areally extended in two dimensions as compared to their thickness. In their most commonly observed form tabular grains have two opposed triangular or hexagonal major faces and appear to be bounded by (111) crystal faces.
A. Mignot, E. Francois, and M. Catinat, "Flat Untwinned Silver Bromide Crystals Limited by (100) Faces," Journal of Crystal Growth, Vol. 23, (1974), pp. 207-213, report the observation of tabular silver bromide crystals having square or rectangular major faces. The crystals appear to be bounded by (100) crystal faces. These tabular grains were present in emulsions predominantly containing other grain configurations.
Bogg U.S. Pat. No. 4,063,951 discloses a technique for preparing tabular silver halide emulsions containing tabular grains bounded by (100) crystal faces. The tabular grains have two opposed, substantially parallel major faces which are square or rectangular. The tabular grains are prepared from monodisperse seed grains. Upon Ostwald ripening in the presence of ammonia, a known ripening agent, and alkali halide tabular grains are formed having an average aspect ratio in the range of from 1.5 to 7:1. Aspect ratio is the ratio of grain edge length to thickness. From FIG. 4 of Bogg, the coefficient of variations appears to be at least 50.
Wilgus and Haefner U.S. Ser. No. 320,905, filed concurrently herewith and commonly assigned, titled HIGH ASPECT RATIO SILVER BROMOIODIDE EMULSIONS AND PROCESSES FOR THEIR PREPARATION, now abandoned in favor of continuation-in-part U.S. Ser. No. 429,420, filed Sept. 30, 1982, discloses high aspect ratio silver bromoiodide emulsions and a process for their preparation.
Kofron et al. U.S. Ser. No. 320,904, filed concurrently herewith and commonly assigned, titled SENSITIZED HIGH ASPECT RATIO SILVER HALIDE EMULSIONS AND PHOTOGRAPHIC ELEMENTS, now abandoned in favor of continuation-in-part U.S. Ser. No. 429,407, filed Sept. 30, 1982, discloses chemically and spectrally sensitized high aspect ratio tabular grain silver halide emulsions and photographic elements incorporating these emulsions.
Daubendiek and Strong U.S. Ser. No. 320,906, filed concurrently herewith and commonly assigned, titled AN IMPROVED PROCESS FOR THE PREPARATION OF HIGH ASPECT RATIO SILVER BROMOIODIDE EMULSIONS, now abandoned in favor of continuation-in-part U.S. Ser. No. 429,587, filed Sept. 30, 1982, discloses an improvement on the processes of Maternaghan whereby high aspect ratio tabular grain silver bromoiodide emulsions can be prepared.
Abbott and Jones U.S. Ser. No. 320,907, filed concurrently herewith and commonly assigned, titled RADIOGRAPHIC ELEMENTS EXHIBITING REDUCED CROSSOVER, now abandoned in favor of continuation-in-part U.S. Ser. No. 430,222, filed Sept. 30, 1982, discloses the use of high aspect ratio tabular grain silver halide emulsions in radiographic elements coated on both major surfaces of a radiation transmitting support to control crossover.
Wey U.S. Ser. No. 320,908, filed concurrently herewith and commonly assigned, titled IMPROVED DOUBLE-JET PRECIPITATION PROCESSES AND PRODUCTS THEREOF, now abandoned in favor or continuation-in-part U.S. Ser. No. 429,403, filed Sept. 30, 1982, discloses a process of preparing tabular silver chloride grains which are substantially internally free of both silver bromide and silver iodide. The emulsions have an average aspect ratio of greater than 8:1.
Solberg, Piggin, and Wilgus U.S. Ser. No. 320,909, filed concurrently herewith and commonly assigned, titled RADIATION-SENSITIVE SILVER BROMOIODIDE EMULSIONS, PHOTOGRAPHIC ELEMENTS, AND PROCESSES FOR THEIR USE, now abandoned in favor of continuation-in-part U.S. Ser. No. 431,913, filed Sept. 30, 1982, discloses high aspect ratio tabular grain silver bromoioidide emulsions wherein a higher concentration of iodide is present in an annular region than in a central region of the tabular grains.
Dickerson U.S. Ser. No. 320,910, filed concurrently herewith and commonly assigned, titled FOREHARDENED PHOTOGRAPHIC ELEMENTS AND PROCESSES FOR THEIR USE, now abandoned in favor of continuation-in-part Ser. No. 430,574, filed Sept. 30, 1982, discloses producing silver images of high covering power by employing photographic elements containing forehardened high aspect ratio tabular grain silver halide emulsions.